The present invention relates generally to medical devices and methods using the same. More particularly, the present invention relates to the structure of radially expansible luminal prostheses, including stents and grafts.
Luminal prostheses are provided for a variety of medical purposes. For example, luminal stents can be placed in various body lumens, such as blood vessels, the ureter, the urethra, biliary tract, and gastrointestinal tract, for maintaining patency. Luminal stents are particularly useful for placement in pre-dilated atherosclerotic sites in blood vessels. Luminal grafts can be placed in blood vessels to provide support in diseased regions, such as aortic abdominal, and other aneurysms.
Both stent and graft prostheses must meet certain mechanical criteria to function successfully. In particular, such prostheses should be at least partly flexible or articulated (such as rigid sections that articulate relative to one another) over their lengths so that they may be advanced through tortuous body lumens, such as those of the coronary vasculature. In addition, the prostheses should preferably maintain their original length or foreshorten minimally when the prostheses assume an expanded configuration. Further such prostheses must have sufficient mechanical strength, particularly hoop strength, in order to mechanically augment the luminal wall strength and thus assure lumen patency. The ability to meet these requirements is severely limited in the case of cylindrical endoluminal prostheses which are delivered in a radially constrained or collapsed configuration. Such prostheses must radially expand at a target site within the body lumen, so any adaptations which are intended to enhance flexibility will not interfere with the ability to radially expand or to maintain strength once expanded.
Such prostheses, including stents, can suffer from a variety of performance limitations including fishscaling, poor tracking, flaring, and unwanted twisting upon deployment. Fishscaling is a phenomena which occurs when the prosthesis is flexed or articulated during delivery or tracking, resulting in the expanded prosthesis having unwanted outward protrusion of portions of the prosthesis from its surface, thereby increasing the likelihood that the prosthesis will dig into or otherwise engage the wall of the body lumen during delivery and even arrest the progress of the prosthesis and its delivery system to the diseased region (or target site). Poor tracking performance may be exhibited when the prosthesis' ability to pass smoothly through tortuous pathways is below the desired level. Flaring is a phenomena which occurs when the distal or proximal end of the prosthesis are bent outward, assuming a crown-like configuration due to bending forces placed on these elements as the prosthesis passes through tortuous body passageways, often resulting in the same deleterious effects as the previously described fishscaling phenomenon, injuring or traumatizing the blood vessel wall as the prosthesis is delivered or tracked within the blood vessel. A common problem with many of the current devices is their being twisted upon or after deployment in the lumen, resulting in unwanted deformation. The unwanted twisting may occur during the deployment of the device. Often, the devices, when for example deployed by an expandable member such as a balloon, is first expanded at its two ends with the midsection, usually at the center, of the device exhibiting an inward crease with its peak pointing inward in the luminal direction. Such inwardly facing peaks then result in a smaller local inner diameter of the device, leading to obstruction of the lumen.
Accordingly, it would be a significant advance to provide improved devices and methods using the same. This invention satisfies at least some of these and other needs.